The present invention relates to vehicle door latches. In particular, this invention relates to a vehicle door latch having a two stage crush zone.
Vehicle door latches must meet specified safety standards. In the United States of America, the latch must meet Federal Motor Vehicle Safety Standard (FMVSS) 206 which requires that the latch and striker assembly shall not separate when a high force is applied. For testing, the latches are loaded to resist loads in the range of 8,900 to 10,700 N, which results in reaction forces for the ratchet and the pawl pins of between 20,000 and 30,000 N. However, in normal use conditions, the latch experiences loads in the range of 100 to 300 N which corresponds to a seal force. As a result, conventional latches arc over-designed in size and cost.
The disadvantages of the prior art may be overcome by providing a latch which will meet all of the design criteria, but will have a predictable and controlled deformation during high load conditions to modify force directions and locations to the strongest portions of the latch and thereby resist separation.
More particularly, a latch is provided which has a housing and a ratchet pivotably mounted to the housing by a rivet for rotation about a first axis between a latched and an unlatched configuration. The housing has a slot extending through it with an arcuate portion generally coaxial with the first axis and a first radial portion extending generally radially away from the first axis. The latch further has a pawl assembly with a roller extending through the slot and mounted to the housing for movement of the roller relative to the ratchet between the first arcuate portion and the first radial portion of the slot. The roller has a roller axis. The rivet is deformable to allow the ratchet to rotate about the roller axis upon the ratchet being exposed to an unlatching force above a predetermined level. A flange extends from the housing across the ratchet to limit pivotal movement of the ratchet about the roller axis.
The roller may be mounted to the housing by a pair of wheels, one on either side of the ratchet, and rotatable relative to the housing about a second axis generally parallel to the first axis.
The latch may include a ratchet spring acting between the ratchet and the housing for urging the ratchet toward the unlatched configuration.
The latch may also have a pawl spring extending between the housing and at least one of the wheels for urging the roller toward the arcuate portion of the slot.
The latch may include an actuator having a Bowden cable with an outer portion fixedly secured to the housing and an inner connected to the pair of the wheels for rotating the pair of wheels to move the roller into the arcuate portion of the slot.
The ratchet may have a second radial portion spaced apart from the first radial portion and extending generally radially from the first axis the the roller may engage the second radial portion to retain the ratchet in the unlatched configuration. The second radial portion may further have a tapered comer along one side thereof to guide the roller into the arcuate portion of the latch in response to a force tending to move the ratchet from its unlatched towards its unlatched configuration.
The latch housing may include a front housing, a rear housing generally parallel to and spaced apart from the front housing, a front mounting plate adjacent the first housing and a rear mounting plate adjacent the rear housing. The ratchet may be mounted between the front and rear mounting plates and each wheel of the pair of wheels may be rotatably mounted to a respective of the front and rear housings.
The flange may be defined by at least one of the front and rear mounting plates.
The ratchet spring may be mounted between the front housing and front mounting plate and the front housing provided with a recess for accommodating the ratchet spring. The pawl spring may be mounted between the rear housing and the rear mounting plate provided with a recess for accommodating the pawl spring.
The rivet may extend between and be secured to the front and rear housings.